1. Field of the Invention
The present invention relates to technology for reducing minute interference unevenness of an optical film disposed at the viewing side of a three dimensional (3D) image display device, and a polarizing plate, an image display device, and a 3D image display system each utilizing the same.
2. Background Art
A 3D image display having a λ/4 plate in front of the display panel at the viewing side has been proposed. The λ/4 plate is disposed on a surface, at the viewing side, of the display panel together with a polarizing film for the formation of a circularly polarized image. The in-plane slow axis of the λ/4 plate for this purpose should be controlled in a specific direction in relation to the absorption axis of a polarizing film. Furthermore, in a passive glasses type, a patterned λ/4 plate having alternately-disposed patterns which have orthogonal in-plane slow axes to each other needs to be used. The in-plane slow axes could be readily controlled if a λ/4 plate can be manufactured with a liquid crystal composition. The in-plane slow axis of a retardation layer formed of a liquid-crystalline compound is typically controlled with an alignment layer.
An optical film having a retardation film composed of an alignment layer and a liquid-crystalline compound on a support made of a transparent film has widely been used as an optically-compensatory film in a liquid-crystal display device. Since the optically-compensatory film is disposed between a liquid crystal cell and a polarizing film, any interference at the interface between an alignment layer and a retardation layer does not affect its display performance. Accordingly, in the optically-compensatory film having such a structure, issues concerning interference at the interface between an alignment layer and a retarding layer has been rarely studied. However, in the form of the use described above, i.e. a configuration of the optical film disposed in the exterior, at the viewing side, of the polarizing film, interference due to difference in refractive indices at the interface between an alignment layer and a retardation layer may affect the display performance.
Uneven interference is generally known to occur in a laminate composed of multiple optical thin films, and it can be reduced by achieving a uniform thickness of each optical thin layer or reducing the difference in refractive indices at the interface. However, complete elimination of the uneven thickness is technically difficult, and a reduction of the difference in refractive indices is also difficult because it restricts the scope of choice for usable materials. Although a light scattering layer disposed on or in the laminate can reduces uneven interference, a light scattering layer disposed at the viewing side of an image display device has disadvantages such as clarity loss on the image display surface and a decrease in the image contrast.
It is well known that uneven interference can be attributed to an uneven thickness of a cell gap or a liquid crystal layer since many optical thin layers, such as a pixel electrode layer, alignment layer, and color filter, laminated on the inner face of a glass substrate in a liquid cell of a liquid crystal display device. Measures to solve this problem are proposed (for example, JP-A-4-166915 and JP-A-2000-231109).